= Real-time polymerase chain reaction
{wiki}
Also known as: Quantitative PCR (qPCR).
Like PCR, but the amplification machine measures the concentration of DNA at each step.
This describes one possible concentration detection method with <fluorescence>[fluorescent] molecules that only become fluorescent when the DNA is double stranded (https://en.wikipedia.org/wiki/SYBR_Green_I[SYBR Green])
\Video[http://youtube.com/watch?v=YhXj5Yy4ksQ]
{title=Polymerase Chain Reaction (PCR) - Quantitative PCR (qPCR) by Applied Biological Materials (2016)}
This allows you to predict the exact initial concentration by extrapolating the exponential curve backwards.
TODO: vs non-real-time PCR. Why can't you just divide by 2 for every heating step to reach back the original concentration? Likely the reaction reach saturation at an unknown step.
TODO: vs non-real-time PCR in medical diagnostics: do you really need to know concentration for diagnostics? Isn't it enough to know if the virus is present or not?